Electrostatic printing apparatus



y 1965 c. J. YOUNG 3,195,430

ELECTROSTATIC PRINTING APPARATUS Filed Dec. 28, 1960 2 Sheets-Sheet 1 [I22 z; 5 ll /4 I ll I 1' L 191 \C INV EN TOR.

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ITMAWEY July 20, 1965 c. J. YOUNG 3,195,430

ELECTROSTATIC PRINTING APPARATUS Filed Dec. 28, 1960 2 Sheets-Sheet 2 4!Fg if 10 INVEN TOR.

United States Patent O 3,195,430 ELECTROSTATIC PRINTING APPARATUSCharles J. Young, Princeton, N.J., assignor to Radio Corporation ofAmerica, a corporation of Delaware Filed Dec. 28, 1960, Ser. No. 78,9306 Claims. (Cl. 9'51.7)

This invention relates generally to improved electrostatic printingapparatus and more particularly to such apparatus including improvedmeans for applying liquid developer compositions t electrostatic images.

In the art of electrostatic printing, electrostatic images are producedon the surface of an insulating material. Such images comprise a patternof electrostatic charges on the surface. Visible images are commonlyproduced therefrom by applying across the surface a dry mixture offinely-divided developer particles and substantially larger carrierparticles. The developer particles deposit in charged areas to produce avisible image in substantial configuration with the pattern of charges.Several methods of producing Visible images are described in ElectrofaxDirect Electrophotographic Printing on Paper, by C. J. Young and H. G.Greig, RCA Review, December 1954, vol. XV, No. 4.

The recording element may comprise almost any insulating surface but,preferably, the recording surface is also photoconductive to enable therecording of light images. Recording elements comprising photconductiveselenium coated plates are described in US. Patent 2,297,691, issuedOctober 6, 1942, to C. F. Carlson. Re-

cording elements comprising photoconductive coatings on paper aredescribed in the aforementioned Young and Greig publication.

A so-called liquid process for developing electrostatic images has beenproposed in which the solid developer particles are suspended in aninsulating carrier liquid. Liquid development methods provide manydistinct advantages over the use of dry developer mixtures and othermethods of developing electrostatic images for some applications.Basically, the liquid developer consists of finely-divided developerparticles dispersed in an insulating liquid. This developer can beflowed over a surface bearing an electrostatic image or the surface canbe immersed in a tray of liquid developer. It can also be sprayed orrolled onto the surface. A liquid developer process for charge images isdescribed in greater detail by K. A. Metcalf and R. J. Wright in a paperentitled Xerography, published in the Journal of the Oil and ColourChemists Association, November 1956, vol. 39, No. 11, London England andin another paper entitled Liquid Developers for Xerography published inthe Journal of Scientific Instruments, February 1955, vol. 32.

Although the above-rnentioned liquid development processes are suitablefor many purposes, it has been found that they have at least one seriousdeficiency. When producing a visible image by deposition of developerparticles from a liquid onto a charged surface, particles adhere in thebackground areas as well as in the image areas on the surface.Background areas are those areas on the surface bearing little or noelectrostatic charge and hence, are those areas in which deposition ofdeveloper particles is unwanted. Such spurious deposit in non-imageareas results in a spotted or mottled background on the finished printwhich, in many applications, is unsatisfactory. This effect is even morepronounced when attempting to reproduce fine detail. The morefinely-divided the developer particles are, the greater the spuriousdeposition in background areas.

In addition to the foregoing, it has been found that when images aredeveloped with a liquid composition carried on a roller, second andsubsequent rotational cycles ice of the roller cause ghost images to beoffset printed on a recording medium by the roller.

It is a general object of this invention to provide improvedelectrostatic printing apparatus.

A further object of this invention is to provide improved appara-tus forapplying liquid developer compositions to electrostatic images.

A still further object is to provide improved roller apparatus fordeveloping electrostatic images on recording members with substantialreduction or elimination of undesirable offest printing of ghost imagesthereon.

These and other objects are accomplished in accordance with thisinvention which provides electrophotographic apparatus including meansfor charging the surface of an electrophotographic member, means fortransporting the member through an exposure region, and a developermechanism adjacent the exposure region comprising a developer rolleradapted to have the electrophotographic member contact therewith andmeans for washing said roller with liquid developer composition in amanner to substantially reduce or eliminate offest printing or ghostimages deriving from the previous development of the precedingelectrostatic images.

Other objects and advantages will be apparent from the followingdetailed description to be read with reference to the accompanyingdrawings wherein:

FIG. 1 is a side elevational, cross-sectional view of the interior of anelectrostatic printing apparatus made in accordance with this invention;

FIG. 2 is a rear elevational, cross-sectional view of the interior ofthe apparatus of FIG. 1 taken along the line 2-2 thereof;

FIG. 3 is a side elevational view, partly in section, of the developermechanism of FIG. 2;

FIG. 4 is an enlarged side view partially in cross section of a portionof the developer mechanism of FIG. 3.

Similar reference characters are applied to similar elements throughoutthe drawings.

A compact photocopy apparatus in accordance with this invention isillustrated in FIG. 1. The apparatus is designed with a portion of thetop of the housing thereof forming an inverted V-shaped roof. ThisV-shaped structure is adapted, as shown, to support a book 11 so that apage thereof which is to be copied is in contact with a transparentplate 13. A hinged plate 14 is provided to insure that the page to becopied is firmly held against the transparent plate 13. A single sheet,such as a letter, could be equally well held in place by the hingedplate 14. The page of the book is illuminated through the transparentplate 13 by means of a light source 15 and a reflector 17.

The light source 15 may comprise one or more pencil shaped horizontallamps. Well suited for the purpose are lamps such as 500 watt tungstenfilament quartz tubes which contain traces of iodine. The iodine in thelamp functions to catch tungsten particles which evaporate duringoperation and to return those particles to the filament. Such a lamp isproduced by the General Electric Corporation, catalogue No. SOOTS'Q/CL.The reflector 17 conveniently comprises a segment of a 6" hollowcylinder, the inside of which is polished to a high degree. Since thedistance from the light source 15 to the bottom edge of the plate 13 ismuch less than the distance of the light source 15 to the top edge ofthe plate 13, the refiector 17 is positioned to concentrate reflectedlight toward the upper portion of the transparent plate 13 so that theentire area under the plate is uniformly illuminated.

Light reflected from the page of the book 11 is concentrated throughlens 19 to impinge upon the mirror 21. The light is then reflected fromthe mirror 21 upwardly and focused on an exposure plane 23. A shutter 25is 3 provided in the light path between the mirror 21 and the exposureplane 23 in order to prevent any light from entering the right handcompartment 27 of the copier apparatus except when exposure is desired.

Further details of the internal structure of the compartment 27 areillustrated in FIGURE. 2. A supply roll of photo-sensitive webbing ismounted in the lower portion of the compartment 27. The webbing 3% onthe supply roll may comprise, for examole, electrophotographic papersuch as is described in the aforementioned Young and Greig publication.The paper 3% is fed from the supply roll 29 over an idler roller 31through a double corona charging apparatus 53 and into the exposureplane 23. The paper is then carried partly around one roller of a pairof pressure rollers in a manner so that it reverses its direction and isthen brought out from the copier apparatus under a heat fusing mechanism25;;

in the apparatus as shown in FIGURE 2, the double corona charging unit33 may comprise 2 opposed structures of very fine parallel wires asdescribed in US. Patent 2,922,883, issued to E. C. Giaimo, Jr., and theheat fuser 28 one such as is described in U.S. Patent 2,857,682 to R. G.Olden et a1.

From the charging apparatus 33 the paper is transported into theexposure plane 23 with its photosensitive surface facing downward. Whilethe paper is maintained stationary in the exposure plane 23, the lightimage refiected upward from the mirror 21 will substantially redues oreradicate the charges placed on the paper by the corona unit 33 in thoseareas on which light impinges. As the paper 36 passes over one of thepressure rollers 25, liquid developer composition from liquid developerunit is applied to the other pressure roller 26, which in turn appliesthe liquid developer composition to the paper 3b to produce, in thoseareas thereon which were not struck by light, a visible image ofdeveloper material. This visible image is then fixed to the surface ofthe paper as it passes under the fuser 28.

In FIGURE 3, the developing unit 35 of FIG. 2 is illustrated in greaterdetail. This developer unit includes the two pressure rollers 25 and 26which engage the paper and which are driven to pull the paper from thesupply roller 29 (FIG. 2) through the projection plane 23 shown inFIGURE 2. Liquid developer composition is applied to the upper pressureroller 26 by means of an applicator ll. The developer composition issupplied to the applicator 411 through a pipe 43 (FIG. 3) connected to acentrifugal pump 45. As liquid developer composition is carried by theupper pressure roller 26 into contact with the paper, a turbulent nip asof thedeveloper composition is formed where the roller 26 contacts thepaper. This turbulent nip 46 of developing composition substantiallyenhances development of images on the paper and also enhances clean upof developer material which may adhere in unwanted areas on the paper36. The liquid developer composition not only forms the nip 46 but alsoflows down the surface of the paper 3@ as it is carried over thepressureroller 25. The developer composition is thereby caused to be incontact with a substantial portion of the paper 30 as it is transportedover the roller 25.

Developer composition in excess of that used to develop animage on thepaper drops therefrom into a tray or sump 47 positionedbelow the twopressure rollers 25 and 26. The developer composition collected in thesump 47 is returned to the developer container 44 through a pip 49 whichsurrounds the feed pipe 43. 7

An important feature of the developer unit shown in FIG. 3 is that itcomprises a substantially closed system for developing images on thepaper 3%. Such a closed system makes it possible to use developercompositions which include a highly volatile liquid without resulting inexcessive evaporation of that liquid. Excessive evaporation wouldultimately result in wide variations in the concentration of thedeveloper material in the developer composition.

An example of a suitable, highly volatile developer composition is onewherein finely-divided electroscopic developer particles are dispersedin a liquid carrier of tr1chlorotriliuoroethane.

Example A black pigment is prepared by making two solutions:

Solution one comprises:

6 grams Iosol Black (Cl. Solvent Black 13) 490 grams methanol Solutiontwo comprises:

9 grams Spirit Nigrosine (CI. 50415) 406 to 600 grams methanol Solutionone is poured into solution two with continuous stirring. Gnce thesolutions have been thoroughly mixed and a black, relatively insolublepigment is precipitated, the mixture is filtered and the filter cakeallowed to dry. The dried filter cake is'broken up and dispersed indimethyl polysiioxane liquid having a viscosity of about 2 centistokes.The proportions in this dispersion are about 1 to 10 parts black pigmentto about 20 parts of liquid. It is preferred that the liquid content bekept as low as possible but sufiicient to provide a uniform dispersion.After ball milling the black pigment is classified as to particles size.Particles having a diameter of 74 microns or less are preferred.

7 Also prepared is a solution consisting of:

260 grams dimethyl polysiloxane 200 grams trichiorotriiluoroethane.

About one part by weight pigment dispersion per 10 parts solution isadded to provide a final developer composition.

As images are developed on the paper with the apparatus, theconcentration of developer particles in the container dd will becomedepleted at a greater rate than will the liquid carrier portion thereof.in order to maintain the proportions of components in the liquiddeveloper at a substantially constant level, means are provided forinjecting into the container 4d, metered amounts of a concentrateddeveloper composition. The developer concentrate is contained in a jar51. A reciprocating pump 53 is inserted in the jar 51 and is powered bya solenoid 54. At each stroke of the pump 53 in the jar 51 a smallquantity of developer concentrate is forced through the pipe 55 andinjected into the container 44. it is desirable that the reciprocatingpump 53 be provided with an adjustable stroke whereby the quantity ofdeveloper concentrate injected each time into the container 44 can beregulated. It is also desirable that the solenoid be energized, ifdesired, each exposure cycle or if desired once each two cycles or onceeach five cycles or so.

A sutable developer concentrate may be prepared by dispersing developermaterial such as that described heretofore in a dimethyl polysiloxane ina proportion of about 20 parts by weight of developer material to partsby weight of a dimethyl polysiloxane having a viscosity from 0.6 toabout 3 centistokes.

In FIG. 4 further details are provided of a suitable construction forthe applicator member 41 of FIG. 3. The applicator member is here shownas comprising a metalhead til which will have a length equal to thelength of the paper to be developed. One face 63 of the applicatormember is bevelled so that it can be positioned in close proximity tothe pressure roller 26. An elongated U-shaped slot 65 is provided in thehead 61 and into this slot developer composition is supplied underpressure through the pipe 43. 'Near the top of the slot there isprovided an elongated slide 66 having a multiplicity of apertures 67therethrough. These apertures being, for example, holes .040 inch indiameter, counter sunk on one side, and spaced about inch apart alongthe length of the slide 66. By using such a slide, a con-' venient meansis provided whereby, upon removal of the slide 66 from the head 61, boththe slide 66 and the U- shaped slot 65 can be easily cleaned.

It has been found that, in normal operation, development of the image onthe paper as it is carried over the lower pressure roller 25 will causea ghost image to be off-set printed on the upper pressure roller 26 asthe periphery thereof moves away from the paper 30. Unless some meansare provided for removing this ghost image from the upper pressureroller 26, it would again contact the paper and off-set print thereon aghost image which under most circumstances would be undesirable in afinished print. In the embodiment illustrated herein, developercomposition is forced through the apertures 67 in the slide 66 underpressure so that the composition strikes the roller 26 with suflicientforce to substantially obliterate any offset images previously formed onthe surface thereof.

What is claimed is:

1. Reproduction apparatus comprising a camera housing having a bottomportion and a roof portion, said roof portion being formed in the shapeof an inverted V, one leg of said inverted V including a transparentplate, said roof portion having an apex that is more distant from saidbottom portion than the edges of said inverted V, whereby an opened'book may be supported on said roof portion by only the legs of saidinverted V, illumination means Within said housing for projecting lightonto said transparent plate and material positioned thereon for copyingpurposes, means within said housing for focusing a light image reflectedfrom said material to be copied onto a focal plane, said means includinga mirror and a lens positioned in the light path between said mirror andsaid transparent plate, means for supporting a supply roll ofphotosensitive sheet material means for guiding said sheet material intosaid focal plane, means for moving said sheet material from said supplyroll into said focal plane and out of said focal plane means forenergizing said illumination means to produce a latent image on saidphotosensitive sheet material and means for applying liquid developercomposition to said sheet material to develop said latent image.

2. The reproduction apparatus of claim 1 including a hinged plateadjacent said transparent plate for holding subject matter to be copiedagainst said transparent plate.

3. Reproduction apparatus comprising a camera housing having a bottomportion, a partition in said housing dividing it into first and secondcompartments, said first compartment having a roof portion thereofformed in the shape of an inverted V, one leg of said inverted Vincluding a transparent plate, said roof portion having an apex that ismore distant from said bottom portion than the edges of said inverted V,whereby an opened book may be supported on said roof portion by the legsof said inverted V, illumination means within said first compartment forprojecting light onto said transparent plate and material positionedthereon to be copied, means within said housing for focusing a lightimage reflected from said material to be copied onto a focal planewithin said second compartment, said means including a mirror in saidsecond compartment for reflecting light onto said focal plane and a lensmounted in an aperture in said partition in the light path between saidmirror and said transparent plate, means for supporting a supply roll ofphotosensitive sheet material means for guiding said sheet material intosaid focal plane, means for moving said sheet material from said supplyroll into said focal plane and out of said focal plane, means forenergizing said illumination means to produce a latent image on saidphotosensitive sheet material and means for applying liquid developercomposition to said sheet material to develop said latent image.

4. The reproduction apparatus of claim 3 including shutter means in saidsecond compartment in the light path between said lens and said focalplane.

5. Electrophotographic apparatus comprising: a camera housing having abottom portion and a roof portion, said roof portion being formed in theshape of an inverted V, one leg of said inverted V including atransparent plate; said roof portion having an apex that is more distantfrom said bottom portion than the edges of said inverted V, whereby anopened book may be supported on said roof portion by only the legs ofsaid inverted V, illumination means within said housing for projectinglight onto said transparent plate and material positioned thereon to becopied; means within said housing for focusing a light image reflectedfrom said material to be copied onto a focal plane, said means includinga mirror and a lens positioned in the light path between said mirror andsaid transparent plate; means for supporting a supply roll ofelectrophotographic sheet material means for guiding said sheet materialinto said focal plane, means for moving said sheet material from saidsupply roll into said focal plane and out of said focal plane, meansadjacent said focal plane for producing a substantially uniformelectrostatic charge on one surface of said sheet material; means forenergizing said illumination means to produce a latent electrostaticimage on said electrophotographic sheet material :and means for applyingliquid developer composition to said sheet material to develop saidlatent image.

6. Electrophotographic apparatus comprising: a camera housing having abottom portion, a partition in said camera housing dividing it intofirst and second compartments, said first compartment having a roofportion thereof formed in the shape of an inverted V, one leg of saidinverted V including a transparent plate; said roof portion having anapex that is more distant from said bottom portion than the edges ofsaid inverted V, whereby an opened book may be supported on said roofportion by only the legs of said inverted V, illumination means withinsaid first compartment for projecting light onto said transparent plateand material positioned thereon to be copied; means within said housingfor focusing a light image reflected from said material to be copiedonto a focal plane within said second compartment, said means includinga mirror in said second compartment for reflecting light onto said focalplane and a lens mounted in an aperture in said partition in the lightpath between said mirror and said transparent plate; means within saidsecond compartment for supporting a supply roll of elec trophotographicsheet material; means for guiding said sheet material into said focalplane; means for moving said sheet material from said supply roll intosaid focal plane and out of said focal plane; means adjacent said focalplane for producing a substantially uniform electrostatic charge upon asurface of said sheet material; means for energizing said illuminationmeans for producing a latent electrostatic image upon said sheetmaterial; means for applying a finely-divided developer material to saidlatent electrostatic image to produce therefrom a visible image andmeans for fixing said visible image to said electrophotographic sheetmaterial.

References Cited by the Examiner UNITED STATES PATENTS 1,313,098 8/19Leumann 1l8-259 2,227,850 1/41 Steinlauf 73 2,914,996 12/59 Whitman95-1.7 2,927,503 3/60 Zollinger 88-24 2,940,358 6/60 Rosenthal 95-1.72,950,661 8/60 Limberger 951.7 3,003,404 10/61 Metcalfe 95--1.7

EVON C. BLUNK, Primary Examiner.

JOHN M. HORAN, NORTON ANSHER, Examiners.

1. REPRODUCTION APPARATUS COMPRISING A CAMERA HOUSING HAVING A BOTTOMPORTION AND A ROOF PORTION, SAID ROOF PORTION BEING FORMED IN THE SHAPEOF AN INVERTED V, ONE LEG OF SAID INVERTED V INCLUDING A TRANSPARENTPLATE, SAID ROOF PORTION HAVING AN APEX THAT IS MORE DISTANT FROM SAIDBOTTOM PORTION THAN THE EDGES OF SAID INVERTED V, WHEREBY AN OPENED BOOKMAY BE SUPPORTED ON SAID ROOF PORTION BY ONLY THE LEGS OF SAID INVERTEDV, ILLUMINATION MEANS WITHIN SAID HOUSING FOR PROJECTING LIGHT ONTO SAIDCOPYING PURPOSES, MEANS WITHIN SAID HOUSING FOR FOCUSING A LIGHT IMAGEREFLECTED FROM SAID MATERIAL TO BE COPIED ONTO A FOCAL PLANE, SAID MEANSINCLUDING A MIRROR AND A LENS POSITIONED IN THE LIGHT PATH BETWEEN SAIDMIRROR AND SAID TRANSPARENT PLATE, MEANS FOR SUPPORTING A SUPPLY ROLL OFPHOTOSENSITIVE SHEET MATERIAL MEANS FOR GUIDING SAID SHEET MATERIAL INTOSAID FOCAL PLANE, MEANS FOR MOVING SAID SHEET MATERIAL FROM SAID SUPPLYROLL INTO SAID FOCAL PLANE AND OUT OF SAID FOCAL PLANE MEANS FORENERGIZING SAID ILLUMINATION MEANS TO PRODUCE A LATENT IMAGE ON SAIDPHOTOSENSITIVE SHEET MATERIAL AND MEANS FOR APPLYING LIQUID DEVELOPERCOMPOSITION TO SAID SHEET MATERIAL TO DEVELOP SAID LATENT IMAGE.